Jatropha production on wastelands in India: opportunities and trade

Jatropha production on wastelands in India: opportunities and trade-offs for soil
and water management at the watershed scale
Kaushal K. Garg1, Louise Karlberg2, Suhas P. Wani1 and Goran Berndes3
1
RP1- Resilient DryLand Systems, International Crops Research Institute for the Semi Arid Tropics
(ICRISAT), Patancheru 502 324, Andhra Pradesh India
2
Stockholm Environment Institute (SEI), Kräftriket 2B, 106 91 Stockholm, Sweden
3
Department of Energy and Environment, Chalmers University of Technology, Göteborg, Sweden
Abstract
Biofuel production from feedstocks grown on wastelands is considered as a means to
address concerns about climate change and improve energy security while at the same
time provide an additional source of income. Establishment of biomass plantations on
wastelands is likely to affect local livelihoods and can affect surrounding ecosystems by
influencing hydrologic flows and processes such as erosion. We present an assessment of
Jatropha plantation establishment on wastelands, using the ArcSWAT modeling tool.
The assessment was made for a wasteland located in the Velchal watershed, Andhra
Pradesh, India, which recently was converted to a biofuel plantation with Jatropha. The
previous land-use, in this case grazing, could continue in the Jatropha plantations.
Several desirable effects occurred as a result of the land-use conversion: non-productive
soil evaporation was reduced as a larger share of the precipitation was channeled to
productive plant transpiration and groundwater recharge, and at the same time a more
stable (less erosive) runoff resulted in reduced soil erosion and improved downstream
water conditions. A win-win situation between improved land productivity and soil
carbon content was observed for the Jatropha plantations. On the other hand, the results
indicate that at the sub-basin scale, reductions in runoff generation as a result of largescale conversion of wastelands to Jatropha cropping may pose problems to downstream
water users and ecosystems. From a livelihoods perspective, Jatropha production was
generally positive, creating a complementary source of income to the farmers, thus
strengthening the resilience of the local community. In the future, the potential gain from
Jatropha cropping is expected to become higher as cropping systems improve and
growing biofuel markets result in better conditions for biofuel producers.
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Keywords: Jatropha, biofuel, India, evapotranspiration, sedimentation, runoff,
livelihoods, soil carbon, water balance, waste land
1. Introduction
In India, rapid urbanization coupled with industrialization and economic growth drives
increasing energy demand and substantial import of crude petroleum oil71. Since
beginning of the 1990s India’s oil imports has increased more than five-fold and has
considerable influence on the country’s foreign exchange expenditures. The Indian
economy is expected to continue to grow with resulting further increase in energy
demand and rising oil imports, projected to reach 166 and 622 million tons by 2019 and
2047, respectively71, which can be compared to the 110.85 million tons of crude oil that
was imported in 2006-0727.
As in many other countries, biofuels are in India considered an option for addressing the
energy security concerns2,28, while also responding to the challenges of climate change
mitigation51. A Petrol blending program mandated 5% ethanol blending of petrol, initially
for selected states and union territories, and in 2006 extended to the whole country
(Ministry of Petroleum and Natural Gas 2009). Programs for stimulating complementary
use of biodiesel to displace petroleum based diesel primarily focused on biodiesel
production based on non-edible oil seeds produced on marginal or degraded lands. The
Government of India approved the National Policy on Biofuels in year 2009 targeting a
20% blend of biofuels with gasoline and diesel by 20171.
1.1 Wastelands in India
The most recent governmental assessment in India classified slightly more than 50
million hectare (ha), or 16% of the Indian land area, as wasteland, including a range of
different land types, e.g., degraded forest land, gullied, ravenous and bedrock-intruded
land, land under shifting cultivation, degraded pasture and grazing land, degraded land
under plantations and mining and industrial land29. Soil degradation processes have
severely reduced the soil productivity and it has been estimated that, on average,
wastelands have a biomass productivity less than 20% of the original potential52.
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Contributing causes include waterlogging, soil salinity/alkalinity, and a combination of
low biomass productivity and excessive biomass removals reducing the soil organic
carbon levels.
A substantial wasteland area consists of degraded lands that are deteriorating due to lack
of appropriate soil and water management, or due to natural causes, and which can be
brought into more productive use. Roughly 40% of the wasteland area has been estimated
as available for forestation58 and about 14 million ha is considered suitable for cultivating
biofuel feedstocks, such as Jatropha78. The National Wastelands Development Board was
established in 1986 with the objective of bringing five million ha of wasteland under fuel
wood and fodder plantations every year. Establishment of biofuel plantations is
considered an option for rehabilitating wastelands, enhancing energy security, and
providing employment opportunities and better livelihoods in rural areas2,51,65,76-78.
Considering that about 35% of India’s inhabitants live below the poverty line and more
than 70% of the poor are small/marginal farmers or landless labourers66, it is essential that
wasteland development provides these socioeconomic benefits.
1.2 Jatropha
Jatropha (Jatropha curcas L.), commonly known as “purging nut” or “physic nut”, is a
tropical, perennial deciduous, C3 plant belonging to the family Euphorbiaceae14,70. It
adapted to perform best under conditions of warm temperatures and, as with many
members of the family Euphorbiaceae, contains compounds that are highly toxic.
Jatropha has its native distributional range in Mexico, C. America and part of S.
America, but has today a pan tropical distribution72. Productivity of Jatropha depends on
precipitation rates, soil moisture availability, soil characteristics including fertility12,20,35,40,
genetics14,37,68, plant age11 and various management factors like pruning, fertilization, and
disease control3,8,23,35,37. Annual yield levels at 2-3 tons dry seeds has been proposed as
achievable in semi-arid areas and on wastelands, while 5 tons ha-1 can be obtained with
good management on good soils receiving 900-1200 mm average annual rainfall
11,19,20
.
Jongschaap et al.,36 reported potential Jatropha yields as high as 7.8 tons dry seed ha-1 yr1
. The decorticated seeds yield about 28-40% oil14, which can be transesterified and used
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for producing biodiesel34,39. Jatropha has not yet undergone breeding programs with
selection and improvement. The productivity varies greatly from plant to plant and
environmental factors are reported to have a dominating role over genetics in determining
seed size, weight and oil content37.
A global assessment of the ecological suitability for Jatropha cultivation under present
and future climatic conditions indicates that high yields should be attainable in both
tropical and hot temperate areas72. Climate change is estimated to reduce average global
yield levels by about 10%, with higher variation at local scale18,30,50. Areas in Southern
Africa (e.g. Zambia), South America (e.g. Argentina, Paraguay), and the northern part of
South and East Asia (e.g., Northern India, Nepal and China) are expected to become
more suitable for Jatropha cultivation in the future72 due to expected reduced frequency
of frost events and cold days and nights33.
Jatropha is considered to be drought tolerant and possible to cultivate on degraded, sandy
and saline soils with low nutrient content60. Nitrogen and phosphorous inputs may be
required for high yields13,31,36 but nutrient recirculates through the leaf fall reduces the
need for fertilizer input78. It is estimated that three-year old Jatropha plants return about
21 kg N ha-1 back to the soil, although the quantity and nutrient content of the fallen
leaves from the Jatropha plant vary with plant age and fertilizer application78. Jatropha
can be grown in broad spectrum of rainfall regimes, from 300 to 3000 mm, either in the
fields as a commercial crop or as hedges along the field boundaries to protect other plants
from grazing animals and to prevent erosion3,40. There is limited knowledge about the
actual water requirement of Jatropha in different agro-ecological regions. However
minimum and optimum rainfall to produce harvestable Jatropha fruits is assessed as 500600 and 1000-1500 mm yr-1 in arid and semi-arid tropics, respectively3,12,72. Furthermore,
assessments of how downstream hydrological processes and sediment transport are
affected by large-scale implementation at the meso-scale (10-10 000 km2) are so far
lacking.
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Even so, from the perspective of water, Jatropha cultivation to provide feedstock for
biodiesel production is in India considered an option for making productive use of
wastelands while at least partly avoiding conflicts with downstream environmental flow
requirements. It is proposed that additional beneficial effects might arise, such as less
erosive storm floods and lower sediment loads in riverine ecosystems, and larger
groundwater formation as a result of improved infiltrability. Using wastelands for
cultivating Jatropha could also help strengthening local livelihoods and income
diversification, given that this is set as a priority for land development43.
1.3 Scope and aim of study
This article report results from a case study of Jatropha cultivation on wastelands in the
state of Andhra Pradesh. The purpose of the Jatropha cultivation was to develop a model
for improving the livelihoods of the poor, through promotion of plantations managed by
user groups on common pool land resources. The aim of the study was to investigate
opportunities and trade-offs of Jatropha cultivation on wastelands from a livelihoods and
environmental perspective, with soil and water as the critical resources. Special emphasis
was placed on water, and hydrological assessments were conducted using the ArcSWAT
tool to analyse the impacts of three different land-use scenarios: (i) a wasteland state
(barren land); (ii) biofuel cropping with Jatropha; (iii) and long-term biofuel cropping
with Jatropha assuming changes in soil carbon content and soil physical conditions.
2. Study area and data
The state of Andhra Pradesh is located in the semi-arid tropics of Southern India and has
some 4.52 million ha of land that is classified as wastelands. This equals 16.5% of the
total geographic area of the state (GOI, 2010). Half the wasteland area consists of
degraded forests, while the rest is covered with scrubs or forms a barren, rocky
landscape. The effects of wasteland conversion to biofuel plantations on water flows and
sedimentation losses are assessed for a formerly degraded wasteland belonging to the
Velchal village, approximately 50 km outside of the city of Hyderabad, in the Manjeera
sub-basin of the Godawari river basin, Andhra Pradesh, (Fig. 1). Due to over grazing by
livestock, a large area of the Velchal watershed (17.28oN latitude, 77.52oE longitude, 645
5
meters AMSL) is classified as wastelands. This wasteland consists of hillock, which is
relatively flat (2-3% slope) and with a sparse vegetation cover of some trees and grass,
and a valley (10-25% slope) covered with various types of bushes and perennial trees.
Soils have been classified as Vertisols with a very shallow soil depth between 10 and 50
cm as an effect of over grazing. The water holding capacity is medium to low, and the
soil organic carbon content is between 0.60 to 1.2 %.
Demographic data of the Velchal watershed shows that more than 44% of the labourers in
the watershed were classified as “land-less” in the year 2005. These people were largely
dependent on casual agricultural labour work or on construction work. In addition, they
often migrated to nearby cities and suburban areas to find work opportunities, where 70%
of them were living in slum areas. The rest of the population in the community (56%) are
so called “marginal farmers”, cultivating rainfed crops on land-holdings less than 2 ha,
and also working as intermittent agricultural labourers65,75.
In the year 2005, the National Oilseeds and Vegetable Oils Development (NOVOD)
together with the ICRISAT consortium, planted Jatropha on 160 ha common property
land belonging to the Velchal village and classified as wasteland. Jatropha seedlings
approximately 60 cm high were planted at 2m x 2m spacing at Velchal watershed. Plants
were grown under rainfed conditions and no irrigation was applied. Soil and water
conservation practices (e.g., bunding and trenches) were implemented to harvest more
rainfall. Fertilization (30 kg N ha-1 and 12 kg P2O5 ha-1) was applied during the Jatropha
planting. Further fertilization (50 kg N ha-1 and 57 kg P2O5 ha-1) was applied in year 2007.
Growth parameters and seed yield of Jatropha crop was recorded. The plantations were
mainly located in the hillock area, although some plantations are also found in the valley.
Before the initiation of the project, landless and marginal farmers were called to a
planning meeting along with the village institutional body (known as Gram Sabha). The
objective of the proposed project, the work protocol, and potential local benefits were
discussed. Self-help groups were formed based on the voluntary interest of poor people in
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need of livelihood opportunities. The group members were trained in various activities
such as nursery raising, planting, harvesting and oil extraction.
Data on crop characteristics to estimate crop water uptake was collected at the ICRISAT
experimental site, a micro-watershed located at the ICRISAT campus in Hyderabad
(17.53oN latitude and 78.27oE longitude) where Jatropha seedlings (3m x 2m spacing)
were planted on 4 ha of land in 2004. Since then, the Jatropha has been cultivated under
good management practices, including fertilization (90 kg N and 40 kg P2O5 ha-1 year-1)
and various agronomic measurements. Seed yield and oil content has been monitored.
The monitored site is characterized by similar climate and rainfall patterns as the
degraded wasteland that was planted with Jatropha in the Velchal watershed. The
topography of the landscape is relatively flat (1-2 % slope). The Vertisol soil that covers
the site has low permeability and a soil depth at approximately 2-3 meters. Rainfall is
highly erratic, both in terms of total amount and distribution over time. The mean annual
rainfall equal to 860 mm, of which 85 % is distributed between June and October.
Pictures in Fig. 2 show Jatropha plantation and its fruiting stage at Velchal and ICRISAT
watershed during year 2010.
3. Material and Methods
Fig. 3 shows a conceptual representation of the hydrological cycle at watershed scale.
Rainfall is partitioned into various hydrological components as defined by mass balance
equation: Rainfall = Out flow from the watershed boundary (Surface runoff + base flow)
+ Groundwater recharge + Evapotranspiration (Evaporation + Transpiration) + Change in
soil moisture storages. Where fraction of rainfall stored into Vadoze zone is known as
green water; and water available into groundwater aquifer and amount of water reached
at river stream is known as blue water16.
A GIS based hydrological model, ArcSWAT (the Soil and Water Assessment Tool), was
used to assess the hydrological processes and yields for the Velchal watershed, for
scenarios with and without biofuel plantations. Since ArcSWAT does not differentiate
7
between transpiration and soil evaporation, a one dimensional, Richards’ based model,
HYDRUS1D, was used to estimate root water uptake under Jatropha cultivation using
data from the ICRISAT BL3 watershed. Fig. 4 shows a flow diagram of the adopted
modeling methodology. ArcSWAT divides rainfall into different hydrological
components based on topography, soil and management practices. Therefore, the
ArcSWAT simulation of the Velchal watershed area results in a partitioning of rainwater
at the soil surface between runoff and infiltration.
To further analyse the division between transpiration and evaporation, the HYDRUS1D
model is used. First, HYDRUS1D was parameterized and calibrated using soil and crop
data from the ICRISAT field experimental station. Secondly, the soil properties were
changed to represent the Velchal watershed, but without changing the crop water uptake
parameterization. The amount of infiltrated water from the ArcSWAT simulation was
then used as input to the HYDRUS1D model, and HYDRUS1D then computed soil
evaporation, transpiration and deep percolation for the Velchal watershed. Both
ArcSWAT and HYDRUS1D assume a second water partitioning point in the soil between
deep percolation to lower soil layers and evaporative flows. This could potentially cause
inconsistencies if the estimates of the water partitioning from the two models of the
Velchal watershed differed substantially. It was however found that the difference
between the models was less than 10%, and the approach combining the two models was
therefore considered as giving a sufficiently accurate representation of the Velchal
watershed.
3.1 ArcSWAT description and inputs
ArcSWAT is a semi-process based hydrological model for analyzing impacts of land
management practices on water flows and sediment loss in complex watersheds5,22. The
model integrates the principal hydrological processes, soil and nutrient transport, and
vegetative growth on a spatial and temporal frame, using a daily to an annual time scale.
Surface runoff from daily rainfall is estimated using a modification of the Soil
Conservation Service curve number (CN) method from United States Department of
Agriculture-Soil Conservation Service4,47 and peak runoff rates are estimated using a
8
modified rational method47. SWAT simulates plant growth by using the generic crop
growth module from the EPIC (Erosion Productivity Impact Calculator) model47. The
crop growth module first calculates the plant growth under optimal conditions, and then
computes the actual growth under stress inferred by water, temperature, nitrogen, and
phosphorous deficiency42. Sediment yield is estimated using the Modified Universal Soil
Loss Equation (MUSLE)81. A detailed description of this model is given by Neitsch et
al.47
ArcSWAT requires three basic files for delineating the watershed into sub-watersheds: a
Digital Elevation Model (DEM), a Soil map and a Land Use/Land Cover (LULC) map.
The DEM for the Velchal watershed was generated from ASTER 30 m remote sensing
data. Only the area marked as “plantation” in Fig. 1 was included in the model set-up. A
soil map of the watershed was prepared by collecting soil samples on a grid structure of
approximately 200 m (Fig. 1). Undisturbed soil cores (34 cores) were taken for
measuring bulk density. Other physical properties such as texture, gravel content, organic
carbon, field capacity and permanent wilting point were estimated in the laboratory.
Table 1a summarizes details of soil physical properties of the Velchal watershed.
A rainfall station (Fig. 1) was installed in the Velchal watershed in the year 2010. In
addition, ICRISAT data of daily rainfall, wind speed, relative humidity, solar radiation
and air temperature were used as meteorological input to the model. Locations of checkdam storage structures were obtained from GPS readings and their surface area and
storage volume were measured. All together 6 reservoirs were created (Fig. 1); their year
of construction and other salient features (i.e., surface area and total storage capacity)
were provided as inputs into model. Rainfed Jatropha is planted in the whole area
included in the analysis. Moreover, some of the parameters values (e.g. soil loss
parameters) were based on a previous study21 of a nearby watershed, Kothapally (Fig. 1),
located in the Musi catchment (Table 1a).
ArcSWAT was subsequently calibrated based on reservoir-volume data. The water level
in two reservoirs (Check dam 1 and Check dam 2 in Fig. 1) were monitored daily
9
between September and November, 2010, and translated into water volumes of the
reservoirs based on information on the area of the dams. These check dams are the largest
dams in the study area and have a storage capacity in the range 3000-5000 m 3. The check
dams are not related to the biofuel plantations project per se, but were constructed for the
purpose of flood prevention and improved groundwater storage. Calibrated parameters
were related to surface runoff processes (CN) and base flow (REVAP_MN, GWQMN)
(Table 1a). Important parameters required for simulating crop growth were taken from
agronomical measurements and chemical analyses78 at the BL3 ICRISAT experimental
site (Table 1a) and from past studies3,6. Seed yield data for Jatropha was collected for a
three year period from year 2008 and 2010 in Velchal, and used to validate simulated
results.
3.2 HYDRUS1D description and inputs
HYDRUS1D is a one-dimensional hydrological model for simulating movement of
water, heat, and multiple solutes in variable saturated media63. This model numerically
solves the Richards’ equation for saturated-unsaturated water flow, and the Van
Genuchten-Mualem, single porosity hydraulic module was selected for simulating water
flows. Related soil hydraulic parameters (i.e. θr, θs, n, α and Ks) were estimated from
neural network prediction (inbuilt in the public domain model HYDRUS1D, version
4.14) using basic soil physical properties like texture, bulk density, soil moisture content
at field capacity and permanent wilting point59 for different soil layers, which had been
measured in the field (Table 1b). The parameters θr, θs are the moisture content at
residual and saturated level, n and α are the shape parameters of the soil water retention
curve and Ks is the saturated hydraulic conductivity of the soil profile, respectively. A soil
profile of 220 cm was defined in the simulation environment and divided into four layers
system based on measured soil physical properties. Upper boundary conditions (rainfall,
potential evapotranspiration and leaf area index) had been measured in the field for the
simulation period, and were provided to the model on a daily time-step. Free drainage
conditions were assumed as the lower boundary condition. A root water uptake module
developed by Feddes17 was selected in present study. The model was run for the period
October 2005 to October 2008.
10
Soil moisture data at different soil depths had been collected using a neutron probe at 10
locations in the BL3 watershed with a 15 day interval since Oct 2005 onwards and was
used to calibrate the model. Initially, parameters governing root water uptake of Jatropha
was assigned from the default dataset of HYDRUS1D for pasture growth (Table 1b), but
were subsequently modified by comparing observed soil moisture with observed data at
different soil layers (22, 37, 52, 82, 112 and 142 cm) during manual calibration. After
calibration, the plant water uptake parameters were maintained, while the soil
characteristics were changed to represent the Velchal watershed instead (Table 1b).
Thereafter the re-parameterised model was run with the simulated infiltration amounts
from the ArcSWAT simulation of the Velchal watershed as soil water inputs at the soil
surface.
3.3 Model Performance
The simulated reservoir volume was similar to measured volumes (correlation coefficient
= 0.97) after calibration (Fig. 5a). The Root Mean Square Error (RMSE) of prediction is
about 350 m3, which is less than 8% of total storage capacity of the check dams,
indicating good model performance. Simulated Jatropha yields (dry seed) ranged from
0.4 tons ha-1 to 0.75 tons ha-1, and correspond well to what was harvested at selected
locations of the Velchal biofuel plantation. Moreover, the calibration results obtained
from HYDRUS1D for the BL3 ICRISAT watershed show good correlation between
simulated and observed data (Fig. 5b). The overall RMSE of soil moisture was 0.04 cm 3
cm-3, while the correlation coefficient ranged between 0.64 and 0.85.
3.4 Scenario development and simulation protocol
The calibrated SWAT set-up was run for a 10 year time period (2001 to 2010). Results
are presented for dry, normal and wet years according to the following classification
(Indian Meteorological Department, Pune, India; http://www.imdpune.gov.in):
•
Rainfall less than 20% of the long term average = dry;
•
Rainfall between -20% to +20% of the long term average = normal;
•
Rainfall greater than 20% of long term average = wet.
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The annual average rainfall of the study area is 910 mm between period from year 2001
and 2010. Three scenarios were analyzed in the study:
i)
The “Wasteland” scenario represents the situation where the landscape is in a
degraded stage. Soils are highly eroded and poor in organic matter and have
poor water holding capacity. Bushes and seasonal grasses dominate the
landscape, which is used for grazing.
ii)
The “Current Jatropha” scenario represents the situation where Jatropha is
cultivated and some soil and water conservation measures (insitu
interventions) are implemented. Leaf fall, stem and other bush/tree biomass is
being added to the soil mainly at dormancy period. Jatropha seeds are
harvested by the local community.
iii)
The “Long-term Jatropha” scenario represents a thought situation where the
conditions in the “Current Jatropha” scenario have been maintained for long
period of time, leading to increased soil organic matter and changed soil
characteristics what regards, e.g., infiltrability and soil water holding
capacity78.
The Wasteland scenario was created by removing the current vegetation cover in the
ArcSWAT parameterization, while the parameterization procedure of the Current
Jatropha scenario was done as described above21. Finally, the Long-term Jatropha
scenario was parameterized based on modifying selected parameters as described in
Table 1c: a) 20% increase in soil carbon content (same as for the long-term biofuel
plantations at the ICRISAT experimental station); and b) changed soil characteristics
(parameterisation taken from the in-situ soil water management scenario in the nearby
Kothapally watershed, as described in Garg et al.21
4. Results
4.1 Impact of Jatropha plantation on water balance
The water balance for the area under study differs substantially depending on land use
and amount of annual average rainfall (Fig. 6a). In general, a larger share of the total
rainfall forms runoff during wetter years compared with drier years. For the Wasteland
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scenario, runoff constituted 40-60% of total rainfall amount, while for the Long-term
Jatropha scenario, the corresponding figure is 20-40%. Between 4 and 17% of total
rainfall was going to groundwater recharge, while the remainder was transferred to the
atmosphere through evaporation or evapotranspiration.
A comparison of the different land management scenarios shows that more than 50% of
the non-productive soil evaporation in the Wasteland scenario is shifted into productive
transpiration in the two Jatropha plantation scenarios (Fig. 6a), while the total amount of
evapotranspiration (ET) is relatively similar in all three scenarios, except during dry
seasons when ET is higher in the Jatropha scenarios, and even higher under improved
soil conditions. Groundwater recharges doubles in the Jatropha scenario and quadruples
in the Long-term Jatropha scenario, compared with the Wasteland scenario (Fig. 6a). As
a result of higher ET and groundwater formation, runoff formation decreases in the
Jatropha scenarios, in particular during dry years. In the Wasteland scenario, runoff
constitutes around 40% of the total rainfall during dry years while the corresponding
figure for the Current Jatropha scenario is around 30%, and even lower (down to 20%)
for the Long-term Jatropha scenario. Such a large reduction in outflows from the
watershed at a time when the average rainfall amount is low might have negative impacts
on downstream ecosystems and water users.
The distribution of the water balance components over the year also varies with land-use
(Fig. 6b). While the total ET is lower for the two Jatropha plantation scenarios during
the dry season (December-March), it becomes higher during the wetter parts of the year.
This means that the annual fluctuations in runoff and groundwater generation are smaller
in the Jatropha plantation scenarios, compared with the wasteland scenario.
Runoff generated from the watershed consists of two components: i) surface runoff and
ii) base flow generation. It was found that even though the total runoff was significantly
lower with Jatropha plantations compared with the waste-land condition, base flow was
in fact higher with Jatropha plantations (Fig. 6c). On an average, the total amount of base
flow generation in the Wasteland scenario was only 70% of the base flow in the Jatropha
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scenarios; however, total runoff was 40% larger for the wasteland state compared with
the long-term Jatropha scenario.
Land management also affects runoff intensity. In general, higher runoff intensities were
predicted for the wasteland state, compared with Jatropha plantations (Fig. 6d). The
results show that the average daily run-off intensity decreased by 12 % for the current
Jatropha plantation, compared with the wasteland condition, and is likely to decrease
even further with continued Jatropha cropping (the Long-term Jatropha scenario had 39
% lower runoff intensity than the Wasteland scenario).
4.2 A comparison of water balance among BL3 ICRISAT and Velchal watershed
A comparison of water balance components between the well managed ICRISAT BL3
watershed and the Velchal community site (“current Jatropha” scenario) shows (Table 2)
that a larger part of the rainfall formed green water flows (i.e. evapotranspiration) at the
well managed site (80-90% compared with 40-60% respectively). This means that only a
small fraction (10-20%) of the total rainfall generated blue water flows (runoff and
groundwater recharge) at the ICRISAT BL3 location. During dry years, blue water
generation was lower than green water generation at both sites. The division between
green and blue water components for Jatropha at the well managed site corresponds well
with those observed for many water demanding cereal crops53.
4.3 Sediment transport and soil loss
Currently, the estimated average soil loss in the Velchal watershed is between 10-15 tons
ha-1yr-1. Because the soil depth is low and the available water holding capacity is poor in
the watershed, large runoff is commonly generated during rain, with the capacity to carry
large amounts of sediments. Soil loss was found to increase exponentially with rainfall
intensity, and varied with land-use (Fig. 7a), so that the highest soil loss occurred at high
rainfall intensities under wasteland conditions. Cumulative soil loss generated at the
watershed outlet over a ten year period showed that Jatropha cultivation resulted in a
reduction of the total soil loss amount of nearly 50% compared to the wasteland state
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(Fig. 7b). With improved soil condition (Long-term Jatropha scenario), soil loss
decreased even further.
4.4 Jatropha Growth and crop yield
Crop growth parameters measured at ICRISAT and Velchal during year 2008 are
presented in Table 3. Jatropha seed yields are found below 0.5 tons ha-1 within the three
years of plantation at ICRISAT but afterwards increased substantially. Jatropha seed
yields in the Velchal watershed after year three and onwards varied (0.3-0.8 tons ha -1 yr-1)
depending on rainfall variability78. At the ICRISAT BL3 site, the corresponding figure is
1.0-2.7 tons ha-1yr-1. The relatively poor seed yield in Velchal is due to water and nutrient
stress, as confirmed by model simulations (data not shown). Table 2 shows difference in
soil physical and land management conditions of two experimental sites. Jatropha plants
at the ICRISAT micro-watershed could utilize more green water compared to Jatropha
plants at the Velchal watershed. Moreover, three year old plantations recycled 20.8 Kg N,
2.0 Kg P and 23 Kg K ha-1 through leaf fall (Table 3). This nutrient recycling has an
important role in sustaining the productivity of the landscape and building carbon
stocks2,78.
5. Discussion
5.1 Soil and water related impacts
Wastelands are characterized by sparse vegetation cover, exposing soils to both rainfall
and solar radiation. Large soil losses occur during instances of intensive rainfall, and the
non-productive soil evaporation can be very large due to the lack of vegetative cover. The
results show that under favorable soil management and with a good water supply, the
water uptake of Jatropha is similar to that of many water demanding cereal crops.
However, on wastelands where crop management is quite difficult, Jatropha plantations
might be a better option for enhancing productive water flows and at the same time
protect these areas from further degradation1.
The results from this study confirm the hypothesis that Jatropha plantations on waste
lands can have several positive effects in relation to soil and water:
15
•
Reduced soil losses due to lower erosion rates when the soils are better protected
by vegetation and roots. Besides the on-site benefits this also has the benefit that
sedimentation loads on rivers and other water bodies are reduced;
•
Increased soil carbon content, which changes the soil physical characteristics so
that both water infiltrability and soil water holding capacity increase. The soil
carbon increases also enhances the climate change mitigation benefit by
withdrawing CO2 from the atmosphere;
•
Redirection of non-productive soil evaporation into productive transpiration,
which improves the field level water productivity;
•
Increased groundwater recharge.
A potential risk with Jatropha plantations is reductions in runoff generation resulting in
reduced downstream water availability. In this study, the total runoff amount was
modeled to be 40% larger for the wasteland condition, but despite of this, base flows
were higher when Jatropha was grown and runoff intensities were at the same time
lower, which is generally positive, since it reduces the risks of flooding of cultivated
areas. Higher base flow results in lower differences between high and low flows in rivers,
which again is beneficial from a flood risk perspective. Most likely this is also positive
for the riverine ecosystems, since rivers in this region are perennial and thus requires a
certain amount of base flow to sustain key processes and functions.
Thus, under the conditions existing in the Velchal watershed the establishment of
Jatropha plantations appear to be an attractive option. A larger share of the precipitation
was channeled to productive transpiration and groundwater recharge, and a more stable
(less erosive) runoff improved the downstream water conditions. On the other hand,
maintaining a certain amount of total annual runoff is crucial for the Manjeera dam
located downstream of the watershed (Fig. 1), which is one of the drinking water supplies
for the rapidly growing city of Hyderabad. If Jatropha plantations were implemented at a
large scale upstream, resulting in higher consumptive water use, the concurrent
reductions in runoff, in particular during dry seasons, might result in trade-offs between
upstream and downstream water users, and potentially also impact riverine ecosystems.
16
Downstream water availability is likely to be least affected in good years or high and
moderate rainfall zones but could be an important constraint in dry years or low rainfall
zones of semi-arid tropics9,38,69. Again, this should be weighed against the positive effects
of reduced sedimentation in the rivers and the dam due to the reduced soil loss from
Jatropha plantations. In order to analyze effects of different upstream land-use
alternatives on the various stakeholders in the sub-basin, an integrated assessment of
various land-use and management options for the whole sub-basin area has to be made.
Soil loss and soil degradation might become an increasingly important factor to account
for in the future62,74. It is apparent that soil loss from the fields at rainfall intensities above
30-50 mm day-1 is significant21, in particular for wastelands. Due to climate change, high
rainfall intensities are projected to become more common in different parts of India 46,49,83
and elsewhere in the World7,10,84. Soil loss from the fields can therefore be expected to
increase61,80,85. Once land degradation has begun, the process may eventually become
difficult to halt since the lack of vegetation causing high soil loss makes rehabilitation
more difficult41,48,73,82. Hence, a vicious circle may become established, which is difficult
to interrupt due to the negative feedback mechanisms between canopy coverage, runoff
generation and soil loss. Other studies have shown that Jatropha has the potential to
rehabilitate landscapes that have been badly degraded3,51 and can also induce carbon
sequestering in soils32. For Indian wastelands, an average annual carbon sequestration
rate as 2.25 CO2 tons ha-1 year-1 has been reported for the case of Jatropha20.
5.2 Contributions to improved livelihood conditions
There are several negative consequences of Jatropha has also been assessed at larger
scale of implementation24-26,57. It is not found socially and economically viable to switch
agricultural land into bio-fuel plantation15,44. Conversion of agricultural land to Jatropha
is not found remunerative both in rainfed and irrigated lands in private farms at Tamil
Nadu, India and its potential variability is strongly determined by water access.
Unrealistic claims on yield predictions mainly in low input regions by various
development agencies led to serious conflicts between the state and the farmers, between
socio-economic classes and even within households45.
17
The present study supports the view of above study that does not address to convert
agricultural land into Jatropha land. However, wastelands or degraded lands where crop
cultivation is not feasible, provides an opportunity to cultivate Jatropha through
collective community participation. In current case study, Jatropha cropping has
provided the local community in the Velchal watershed with an additional source of
income, which strengthens the resilience of the village by enabling farmers to operate on
different markets (food and energy). Currently the income from the biofuel plantation is
small in relation to total household budgets. Harvested Jatropha seeds generate an
income of approximately 100 US$ ha-1 year-1 (considering seed yield between 0.5 and 1.0
tons ha-1 after the fourth year and onwards65,78 and Jatropha seed cost as 0.22US$ kg-1 (10
INR kg-1)45,78, which can be compared with incomes from agricultural crops grown in the
area at around 400-500 US$ ha-1 year-1 (assuming a cropping intensity of 150 % and
average crop yields at 1-2 tons ha-1 in arid and semi-arid tropics under rainfed
conditions55,64,79). However, the economic returns from the biofuel plantations will be
higher if the biofuel prices increase in the future. Moreover, the present seed yields are
less than half of the potential yields, which are estimated to be about 2.5 tons ha -1 under
rainfed conditions78. This indicates substantial scope for further yield improvements
through better management practices such as nutrient application coupled with improved
soil and water conservation, and subsequently higher economic returns.
The beneficiaries of the Jatropha plantations on former wastelands in the Velchal
watershed are mainly landless labourers and marginal farmers. There are plans to put an
oil expeller unit for oil extraction and a power-generator unit for electricity production in
the Velchal village65. The electricity generated from this setup is intended to be sold for
commercial purposes in the village itself, thus providing an additional income. Moreover,
this program has also helped to generate other employment opportunities to some of the
women groups by starting plant nurseries and supplying quality seedlings 78. At the same
time the former land-use practice, i.e. grazing, has continued as before in the Jatropha
plantation, but the risk for further degradation is now gone. This means that nobody in
the village lost their customary right due to the Jatropha plantations. Grazing in Jatropha
18
plantations may raises concerns about the potential intoxication of livestock. Toxicity in
Jatropha is due to presence of toxalbumin of nomecurcin (toxin protein) which irritates
to the gastrointestine mucosa and also hemoagglutinating and cause nausea, vomiting,
intense abdominal pain and diarrhea with bloody stool54, however such incidence in study
village has not been reported till date. An additional benefit to the community is higher
groundwater tables, which improves access to water for domestic and agricultural use.
Achten et al.1 thoroughly discussed the benefits of Jatropha cultivation in wastelands at
local scale. After oil extraction seed cake, however, could not be used for animal feed due
to its toxic content but it could potentially be used as fertilizer that also serves as
biopesticides/insecticide and molluscicide simultaneously56. Moreover seed cake could be
used for biogas production through anaerobic digestion before using it as a soil
amendment67.
5.3 Model and data uncertainties
The approach to combine the two modeling tools ArcSWAT and HYDRUS1D causes a
risk for small discrepancies in the estimations of the division between deep percolation
and evapotranspiration. Ideally, both soil evaporation and transpiration should be
calculated explicitly in ArcSWAT, but this was not possible in the current model version.
The parameterization of the different land management scenarios for Velchal was based
on analyses from Kothapally, which is located at a nearby watershed in the Osman Sagar
catchment area as shown in Fig 121. This may lead to some uncertainty in results and
additional validation to support the model parameterization may further improve the
confidence of the modeling results. Even so, the data quality and overall model
performance is judged to be satisfactory for the purposes of this study, and for supporting
the conclusions made.
6. Conclusion
Overall, changes arising from the conversion of wastelands into Jatropha plantations
were desirable from an ecosystem’s perspective at the watershed scale. Non-productive
soil evaporation was shifted to productive transpiration, groundwater recharge improved
and soil loss from the fields was reduced. Moreover, it was found that the soil carbon
19
content increased in the Jatropha plantations over time creating a win-win situation
between land productivity and climate change mitigation.
The results from this study indicate that at the sub-basin scale, reductions in runoff
generation as a result of converting wastelands to Jatropha plantations may pose
problems for downstream ecosystems and water users if implemented on a large area;
however base flow actually improved with Jatropha cropping while storm flows and
sedimentation loads were lower. The net impact of these changes depends on the
characteristics of downstream water users and ecosystems.
At the community level, Jatropha production was generally positive from a livelihoods
perspective. The previous land-use, in this case grazing, could continue in the Jatropha
plantations, which provided a new source of income, thus strengthening the resilience of
the farmers. In the future, the potential gain from Jatropha cropping may become a lot
higher compared with today, as plantation yields increase and demand for petroleum
substitutes such as Jatropha biodiesel grows.
Acknowledgement
The authors would like to thank Dr. A.V.R. Kesava Rao, Scientist, ICRISAT for
providing soil moisture data of the BL3, ICRISAT watershed, and to Mr. Ch Srinivas
Rao for his help in data collection at the Velchal watershed. The authors are grateful to
the watershed community of the Velchal village for participating in the bio-fuel project
and for their support. The authors are also grateful to the funding agency, National
Oilseeds and Vegetable Oils Development, Government of India, for providing
development funds for the Jatropha plantation in the Velchal watershed.
20
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Table 1a. ArcSWAT parameterization.
Parameter
name
Parameter Value
Source
Sand content (%)
SAND
43 (35-50)*
Measured
Silt content (%)
SILT
17 (15-19)
Measured
Clay content (%)
CLAY
40 (34-47)
Measured
Gravel fraction (%)
ROCK
64 (49-90)
Measured
SOL_BD
1.55 (1.4-1.7)
Measured
Available Water Content
(mm H2O/mm soil)
SOL_AWC
0.07 (0.03-0.10)
Measured
Organic carbon (%)
SOL_CBN
0.91 (0.6-1.2)
Measured
Soil Depth (mm)
SOL_Z
350 (120-500)
Surveyed
Saturated Hydraulic conductivity (mm/hr)
SOL_K
1.7-5.9
Estimated by Pedo-transfer
func.59
CN
86
Calibrated
RES_K
8.0
Measured
GW_REVAP
0.1
From Garg et al.21
REVAP_MN
10
Calibrated
GWQMN
20
Calibrated
GW_DELAY
2
From Garg et al.21
CH_EROD
0.5
From Garg et al.21
Channel cover factor (-)
CH_COV
0.5
From Garg et al.21
USLE eq. support practice factor (-)
USLE_P
0.5
From Garg et al.21
ADJ_PKR
0.5
From Garg et al.21
SPCON
0.005
From Garg et al.21
CNYLD
0.022
CPYLD
0.0048
PLTNFR
0.013
PLTPFR
0.0015
Variable (unit)
Bulk Density (g cm-3)
Curve number (-)
Hydraulic conductivity of the reservoir
bottom (mm/hr)
Groundwater revap coeff(-)
Threshold depth of water for revap in
shallow aquifer (mm H2O)
Threshold depth of water in the shallow
aquifer required to return flow (mm H2O)
Groundwater delay time (days)
Channel erodibility factor(-)
Peak rate adjust factor for sediment
routing in the sub basin (-)
Linear parameters for cal. of max. amount
of sediment to be re-entrained during
channel sediment routing
Normal fraction of Nitrogen in (seed) yield
(kg N/kg yield)
Normal fraction of Phosphorus in (seed)
yield (kg P/kg yield)
Normal fraction of Nitrogen in plant
biomass at maturity (Kg N/Kg yield)
Normal fraction of Phosphorus in plant
biomass at maturity (Kg P/Kg yield)
Measured at BL3 ICRISAT
site78
Measured at BL3 ICRISAT
site78
Measured at BL3 ICRISAT
site78
Measured at BL3 ICRISAT
site78
30
Parameter
name
Variable (unit)
Parameter Value
Fraction of tree biomass accumulated each
year that is converted to residue during
BIO_LEAF
0.70
dormancy (-)
Number of years required for tree species
MAT_YRS
4
to full development (Years)
Maximum biomass for a forest
BMX_TREES
10
(tons ha-1)
* Data in parenthesis show minimum to maximum range of parameter value
Source
Measured at BL3 ICRISAT
site78
Achten et al.3;
Bailis and McCarthy6
Achten et al.3;
Bailis and McCarthy6
Table 1b HYDRUS1D parameterization.
Soil Physical Properties of Velchal watershed
Parameter
name
Parameter Value,
Velchal
Parameter Value,
ICRISAT, BL3
Sand content (%)
SAND
43
45.1
Measured
Silt content (%)
SILT
17
16.0
Measured
Clay content (%)
CLAY
40
39.1
Measured
BD
1.55
1.4
Measured
TH33
0.22
0.34
Measured
TH1500
0.16
0.21
Measured
SOL_Z
350
2500
Surveyed
Variable (unit)
Bulk Density (g cm-3)
Moisture at Field capacity (cm
cm-3)
Moisture at permanent wilting
point (cm3 cm-3)
3
Depth of soil profile (mm)
Source
Root Water Uptake parameters, estimated from ICRISAT, BL3 watershed
Variable (unit)
Value of the pressure head below
which roots start to extract water
from the soil (cm)
Value of the pressure head (cm)
below which roots extract water at
the max possible rate.
Value of the limiting pressure head
(cm), below which roots cannot
longer extract water at the max rate
As above, but for a potential
transpiration rate of r2L. (cm)
Value of the pressure head (cm),
below which root water uptake
ceases (usually wilting point).
Parameter
name
Parameters Value
P0
-10
Default
POpt
-25
Default
P2H
-800
Calibrated
P2L
-1500
Calibrated
P3
-16000
Calibrated
Source
31
Table 1c: SWAT parameters modified from current setup to represent improved organic
condition
Parameter in
ArcSWAT
Parameter Value: current
Jatropha scenario
Parameters Value: longterm Jatropha scenario
Available Water Content
(mm H2O/mm soil)
SOL_AWC
0.07 (0.03-0.10)
0.08 (0.03-0.13)
Organic carbon (%)
SOL_CBN
0.91 (0.6-1.2)
1.1 (0.75-1.5)
CN
86
80
GW_REVAP
0.1
0.15
REVAP_MN
10
2
GWQMN
20
120
CH_EROD
0.5
0.4
Channel cover factor (-)
CH_COV
0.5
0.6
USLE equation support
practice factor (-)
USLE_P
0.5
0.6
Variable (unit)
Curve number (-)
Groundwater revap coeff(-)
Threshold depth of water for
revap in shallow aquifer
(mm H2O)
Threshold depth of water in
the shallow aquifer required
to return flow (mm H2O)
Channel erodibility factor(-)
32
Table 2: Comparison of different hydrological components and crop yields between the
ICRISAT BL3 watershed, and the Velchal watershed (“current Jatropha” scenario).
Variable (unit)
Dry Year
(Year 2007)
ICRISAT
Velchal
watershed,
watershed
BL3
Wet Year
(Year 2008)
ICRISAT
watershed, BL3
Velchal
watershed
Inputs
Available water (cm3 cm-3)
(soil moisture at FC-PWP)
0.13
0.07
0.13
0.07
Soil depth (cm)
300
35
300
35
Annual average rainfall (mm)
707
707
1105
1105
Evaporation (mm)
251 (36%)
188 (27%)
265 (24%)
180 (16%)
Transpiration (mm)
400 (57%)
263 (37%)
606 (55%)
262 (24%)
ND
162 (23%)
ND
550 (50%)
ND
95 (13%)
ND
111 (10%)
0.9
0.5
1.1
0.5
Outputs
Outflow (mm)
GW recharge/
Deep percolation (mm)
Jatropha seed yield
(tons ha-1)
FC = field capacity; PWP = permanent wilting point; ND = not determined
33
Table 3: Growth parameters of Jatropha crop and nutrient content in fallen leafs and
Jatropha seeds measured from the experimental sites (Data collected in year 2008,
Sreedevi et al.65; Wani et al.78)
Variable (unit)
Jatropha Tree age (years)
ICRISAT BL3 watershed
3
Velchal watershed
2
Plant spacing
3mx2m
2mx2m
Plant Height (cm)
Branches per Plant (-)
Stem girth at 10 cm height (cm)
Crown Area (m2)
No. of flowering branches (-)
No of inflorences per plant (-)
Female-male flower ratio (-)
No. of Female flowers (-)
Pod bunches per plant
No of pods per plant
Seed yield per plant (g)
100 seed weight (g)
Total seed yield (tons ha-1)
Total oil content (%)
Nitrogen content in Seed (g kg-1)
Phosphors content in Seed (g kg-1)
Potassium content in Seed (g kg-1)
Sulphur content in Seed (g kg-1)
Boron content in Seed (g kg-1)
Zinc content in Seed (g kg-1)
N content in fallen Leaves (g kg-1)
P content in fallen Leaves (g kg-1)
K content in fallen Leaves (g kg-1)
S content in fallen Leaves (g kg-1)
B content in fallen Leaves (g kg-1)
Zn content in fallen Leaves (g kg-1)
Seed Yield measured from the fourth year
120 (64-196)*
8 (1-38)
21 (6-44)
0.9 (0.5-4.1)
3 (1-7)
3 (1-8)
(4-17)
(2-45)
(1-7)
(3-90)
(28-280)
(44-72)
(0.2 -0.5)
34 (27-38)
22.2
4.8
8.1
1.4
0.015
0.017
9.5
0.7
10
0.94
0.034
0.024
86 (50-114)
5 (2-7)
15.6 (9.2-20.3)
0.1
-
1.0-2.7
onwards (tons ha-1)
* Data in parenthesis show minimum to maximum range of parameter value
0.3-0.8
34
List of Figures
Fig. 1: Location of Study area
35
Fig. 2: Picture showing Jatropha crop and its fruiting stage at Velchal and ICRISAT
watershed during year 2010.
36
Fig. 3: Conceptual representation of hydrological cycle and different hydrological
components at watershed scale.
37
Fig. 4: Flow diagram of adopted modeling methodology.
38
250
Simulated (Checkdam-1)
Observed (Checkdam-1)
Simulated (Checkdam-2)
Observed (Checkdam-2)
Rainfall
Correl coefficient (r) =0.97
3
RMSE= 305 m
5000
4000
200
150
3000
100
2000
Rainfall (mm)
Volume of water (cubic meter)
6000
50
1000
0
0
06/09/2010
20/09/2010
04/10/2010
18/10/2010
01/11/2010
Time (days)
Fig. 5a: Observed and simulated water volume in check-dams between period Sept and
Nov 2010.
39
0.4
Correl Coeff. (r) = 0.80
Soil depth= 22 cm
225
0.3
150
0.2
75
0.1
0.0
0
Soil depth= 37 cm
0.4
3
3
Soil Moisture Content (SMC) in cm /cm
300
Daily rainfall (mm)
Rainfall
0.3
0.2
0.1
Correl Coeff. (r) = 0.85
0.0
0.4
Soil depth= 82 cm
0.3
0.2
0.1
Correl Coeff. (r) = 0.76
0.0
Simulated SMC
Measured SMC Soil depth= 112 cm
0.4
0.3
0.2
0.1
Correl Coeff. (r) = 0.64
01/09
10/08
07/08
04/08
01/08
10/07
07/07
04/07
01/07
10/06
07/06
04/06
01/06
10/05
0.0
Time (Date)
Fig. 5b: Observed and simulated soil moisture content at different soil depth in Jatropha
planted area of ICRISAT BL3 watershed from period Oct 2005 to Oct 2009
40
Runoff
GW recharge
Evaporation
Transpiration
100%
Percentage of Rainfall
80%
60%
40%
20%
0%
Waste
land
Current Long-term
Jatropha Jatropha
Waste
land
Dry Year
Current Long-term
Jatropha Jatropha
Waste
land
Normal Year
Current Longterm
Jatropha Jatropha
Wet Year
Fig. 6a: Water balance components of different land management scenarios during dry,
normal and wet (data from 2001 to 2010).
Evaporation from wasteland
90
Evaporation from current Jatropha
Evaporation from long-term Jatropha
Evaporation/Transpiration (mm)
75
Transpiration from current Jatropha
Transpiration from long-term Jatropha
60
45
30
15
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Time (Months)
Fig. 6b: Monthly soil evaporation and transpiration for three different land management
scenarios in Velchal watershed.
41
Dec
700
Base flow
Surface runoff
600
Water yield (mm)
500
400
300
200
100
0
Waste
land
Current Long-term
Jatropha Jatropha
Dry Years
Waste
land
Current Long-term
Jatropha Jatropha
Waste
land
Normal Years
Current Long-term
Jatropha Jatropha
Wet Years
Fig. 6c: Total runoff generation from the watershed, divided up into base flow and
surface runoff, for three different land management scenarios during dry, normal and wet
years (data from 2001 to 2010).
80
Waste land
Frequency (days)
70
Current Jatropha
60
Long-term Jatropha
50
40
30
20
10
0
0.0-0.5
0.5-2.0
2.0-5.0
5.0-10.0
10.0-20.0
>20.0
-1
Runoff intensity (mm day )
Fig. 6d: Frequency of daily runoff intensity, for three different land management
scenarios (data from 2001 to 2010).
42
12
Waste land
Current Jatropha
Long-term Jatropha
-1)
Soil loss (ton ha
10
8
6
4
2
0
0
20
40
60
80
100
120
Daily Rainfall (mm)
Fig. 7a Impact of land management practices on sediment transport under different land
management conditions (data from year 2001 to 2010).
Cumulative soil loss (ton/ha)
400
300
Waste land
Current Jatropha
Long-term Jatropha
200
100
0
2000
2002
2004
2006
2008
2010
Time (Years)
Fig. 7b: Cumulative soil loss (tons ha-1) under different land management conditions
(data from year 2001 to 2010).
43
44